What’s the difference between composer dump-autoload, composer update and composer install?

The above text already explains the difference between those commands, but for fast readers:

• composer install installs the vendor packages according to composer.lock (or creates composer.lock if not present),
• composer update always regenerates composer.lock and installs the lastest versions of available packages based on composer.json
• composer dump-autoload won’t download a thing. It just regenerates the list of all classes that need to be included in the project (autoload_classmap.php). Ideal for when you have a new class inside your project.
• Ideally, you execute composer dump-autoload -o , for a faster load of your webpages. The only reason it is not default, is because it takes a bit longer to generate (but is only slightly noticable)

reference : http://www.developed.be/2014/08/29/composer-dump-autoload-laravel/